Tubular metal structure

ABSTRACT

A tubular metal structure formed from a steel tape converted to tubular shape with the side edges thereof in abutting relation to provide a longitudinal seam which is welded. The tubing may be transversely corrugated to increase the flexibility thereof; the tubing in plain or corrugated from being useful as conduit means or as sheathing for electrical cable. The steel from which the tape is formed has a specified carbon, manganese and silicon content to improve diverse properties of the fabricated tubing, including the welded seam thereof and the welding procedure.

[22 Filed:

- United States Patent 1 Ziemek et al.

[ 1 Jan. 16, 1973 [54] TUBULAR METAL STRUCTURE [75] Inventors: GerardZiemek, Nordmann,

' both of Hannover, Germany [73] Assignee: Riiliel-iind fietallwerliedelioh nungshutte Aktiengesellschalt, Hannover, Germany Jan. 25, 197i211 App]. No.: 109,099

[30] Foreign Application Priority Data Feb. 19, 1970 Germany ..P 20 07590.5

[52] US. Cl. ..l38/l7l [51] Int. Cl. ..H02g 3/04 [58] Field of Search..138/l21,l42,191,171,177

[56] References Cited UNITED STATES PATENTS 1,813,859 7/1931 Lawrence..l38/171 1,829,638 10/1931 Egler ..138/171 2,361,318 10/1944 Orr et a1137/177 2,817,364 12/1957 Crawford ,.138/171 2,870,792 1/1959 Penrose..138/121 Primary Examiner Everette'A. Powell, Jr. Attorney-Philip G.Hilbert [57] ABSTRACT 7 Claims, 4 Drawing Figures Dreyer ..|3s/12| xPATENTEDJAH 16 I975 FIG.4

INVENTQRS Gerhard Z|emek Ger'l' Nordmann ma 5.

AT TORNEY TUBULAR METAL STRUCTURE Steel sheath is commonly used in themanufacture of electrical cables, usually replacing lead sheath. Suchsheath is formed from a steel tape which is continuously formed aboutthe cable core, to tubular form with longitudinally extending butt seamwhich is continuously welded and then corrugated to provide flexibilityfor the cable as a whole.

Also, tubing for the transport of liquids or gases, is also formed fromsteel tape which is converted to tubular form and the longitudinal seamis welded. A second tubing similarly formed may be disposed in coaxialrelation to the first tubing, the annular space between the tubingsbeing continuously filled with a suitable insulating material such as aself foaming resin; the resin being introduced into the annular spaceimmediately before the seam of the outer tubing is welded. Both tubingsmay be corrugated to increased their flexibility.

ln fabricating such tubings, particularly those which are corrugated,the steel tape must have special properties. Thus the tape must lenditself to deep drawing, cold ductility for bending the tubing, and mustshow in the seam weld area resistance to cracking despite deformation asin flexing.

It has been suggested that tapes for such purposes be formed from killedcast steel, which includes deoxidants such as silicon and aluminum.While the deep drawing characteristic of such steel is somewhat reduced,it has other favorable properties. Thus, the fine structure of thekilled steel and its resistance to coarsening the grain after thewelding operation, the weldment zone remains substantially unaffected bythe welding operation, and in contrast with rimmed steel, it retains itsdrawing properties and is readily deformed in the subsequent corrugatingoperation.

However, such known steel sheath has a disadvantage in that elementsegregation occurs during casting and particularly at the edges,producing local enrichments of sulfur, phosphorus, carbon and thelike.These contaminants render the metal somewhat nonhomogeneous, which inturn reduces the welding speed.

Accordingly, an object of this invention is to provide tubular metalstructures, which may be of the corrugated type, for use as cable sheathor conduits, which is derived from a steel having selected modifyingconstituents which provides a high strength weldment area of highflexibility, and further permits fabrication of the structures at highspeeds.

Another object of this invention is to provide tubular metal structuresof the character described, wherein the steel is of the vacuum degassedtype having a determined content of carbon, manganese and silicon.

Other objects of the invention will in part be obvious and in parthereinafter pointed out.

DESCRIPTION OF THE DRAWING FIG. 1 is a longitudinal view of anelectrical cable having a corrugated steel sheath embodying theinvention;

FIG. 2 is a transverse section thereof taken on line 2-2 of FIG. 1;

FIG. 3 is a transverse sectional view showing another embodiment of theinvention; and

FIG. 4 is a transverse sectional view showing a further embodiment ofthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIGS. 1, 2, Cdesignates a sheathed cable embodying the invention. The same comprisesa conventional electrical cable core 10 over which is formed a steelsheath 11. Such sheath is derived from a tape extending longitudinallyand converted to tubular i form about core 10, to provide alongitudinally welded percent together with a small amount of aluminum.

The steel is preferably of the vacuum degassed type, thereby reducingslag formation to a minimum.

Thus, a steel tape made of a steel with 0.03 'percent carbon, traces ofsilicon, 0.35 percent manganese and 0.05 percent aluminum, showedexcellent properties. Such material showed a mean elastic limit of l9.7kp/mm and a mean Vickers hardness of 93 kp/mm and had goodde'formingproperties.

With the foregoing steel tape, reduced current values may be used in thewelding operatiorl, the tape having a thickness of O.4 mm. The averageincrease in welding speed is evidenced in one case with an increase from9 meters/min. to more then l3 meters/min. However, the average increasein welding speed is about 30 percent.

The welding process used may be of the direct current-arc welding typeunder a protective argon atmosphere; together with multiple weldingelectrodes in tandem relation. Thus, with two electrodes in longitudinalsuccession, a welding speed of 19-20 meters/min. was achieved. In suchcases, the guidance of the tape edges to the welding station must be ofhigh precision, suitable guidance means being used for the purpose.

Alternatively, the steel tapeof the instant invention may be used toform tubing T for conduit purposes, the same being derived from tape 15converted to tubular shape with a longitudinal weld seam 16. Also,tubing T, also formed from steel tape as set forth above, is corrugatedas indicated at 17, after being welded as at 18, FIG. 4.

The steel tapes of the instant invention may have a thickness rangingfrom 0.2 mm. to 1.0 mm. The percentages of steel constituents are all byweight.

We claim:

l. A tubular metal structure comprising a thin metal tape converted totubular form with a longitudinally extending welded seam joining theadjacent tape edges, said tape being of steel containing from 0.03 to0.05 percent carbon, 0.3 to l. percent manganese and less then 0.02percent silicon, all by weight, said welded seam having high coldductility.

2. A tubular structure as in claim I wherein said steel further includes0.05 percent aluminum, by weight.

3. A tubular structure as in claim 1 wherein said structure istransversely corrugated.

4. A tubular structure as in claim 1 wherein said tape has a thicknessof from about 0.2 mm to about 1.0 mm.

5. A tubular structure as in claim 1 wherein the carbon content is 0.03percent and the manganese content is 0.35 percent all by weight.

6. A tubular structure as in claim 1 wherein said tape has a thicknessof 0.4 mm. -5

7. A tubular structure as in claim 1 v vherein said tape is formed ofvacuum degassed steel.

2. A tubular structure as in claim 1 wherein said steel further includes0.05 percent aluminum, by weight.
 3. A tubular structure as in claim 1wherein said structure is transversely corrugated.
 4. A tubularstructure as in claim 1 wherein said tape has a thickness of from about0.2 mm to about 1.0 mm.
 5. A tubular structure as in claim 1 wherein thecarbon content is 0.03 percent and the manganese content is 0.35 percentall by weight.
 6. A tubular structure as in claim 1 wherein said taPehas a thickness of 0.4 mm.
 7. A tubular structure as in claim 1 whereinsaid tape is formed of vacuum degassed steel.